Oil-in-water (o/w) or water-in-oil (w/o) dispersions are not stable. Although a dispersion can be obtained by high shear mixing of two incompatible liquids, such as oil and water, they soon separate and form distinct phases. In order to stabilize such dispersions to render them of practical use, an agent is added to the suspension which prevents the dispersed phase particles from coalescing. These agents are generally called emulsifying agents and thus stable dispersions are often referred to as emulsions. Surfactants and dispersants are terms also used for such agents. The terms are often loosely used in the art, but the end effect of such agents is the stabilization, at least to some degree, of a particle, whether it be a solid or liquid particle, dispersed in an incompatible liquid.
Generally, o/w or w/o dispersions are made stable by a combination of surfactants which provide the necessary hydrophilic-hydrophobic balance and a high surface charge so that the internal phase particles or droplets are prevented from a critical close approach to one another, thus avoiding coalescence. Small sized and highly charged particles or droplets are inherent in these dispersions, and they are highly stable. However, the high stability of these emulsions severely limits their usefulness for many applications, such as for treatment of surfaces or as coatings. These emulsions when applied to a surface, in effect, sit on top of the surface with little penetration into the surface. They remain in emulsified form and are broken to deposit the desired phase onto the surface generally by evaporation of the external phase. The high stability of these o/w dispersions also often results in undesirable water sensitivity. With these prior-art emulsions, it is necessary to have a high charge in order to create stability. The zeta potential of the particles in common emulsions is generally in the order of about 60 to 100 millivolts (mv).